Many people were expecting Facebook to make an announcement about a location-based service at f8, but the company didn’t say anything. Instead, it launched the Open Graph, a set of plugins and protocols intended to extend Facebook features to the web. But the protocols include some information about the company’s location plans. Here they are.

Buried in the protocols documentation, Facebook outlines a couple recommendations for how developers should code “meta data” in a way that Facebook can process. As the company describes it in the documentation: “Two commons pieces of information many profile pages have are location and contact information. Below are examples of how you can provide this information as meta data.”

Then it specifies how you code for location: “This is useful if your pages is a business profile or about anything else with a real-world location. You can specify location via latitude and longitude, a full address, or both.”

Specifying location via latitude and longitude is what mobile location services already do. You’ll see many Twitter users grab their coordinates from their iPhones to list their current location in their profiles, for example, through Twitter’s Geolocation API. Facebook could easily allow any location service to automatically provide this data into the Open Graph API. Suddenly, for example, every user of mobile-based check-in services like Foursquare and Gowalla could instantly update their profiles with their location via this meta data.

From there, Facebook could clearly do a number of very interesting things with the location data, given the size of its social graph and the amount of information it knows about people and things they like.

While Facebook hasn’t said anything, rumors of this sort of federated location system has already been leaking out. We expect more news from the company shortly.